1. Field of the Invention
The present invention relates to an electronic flash device with a slave emission function.
2. Related Background Art
Conventionally, an adapter, called a wireless multiple-flash adapter or a slave unit, for wireless-controlling an electronic flash device to emit light is available in this adapter, upon reception of a steep change in light by a light-receiving element, a switching element is turned on in response to this light, and a synchronous signal is output to control an electronic flash device connected to the adapter to emit light. Therefore, in a multiple-flash photographing operation using a plurality of electronic flash devices for illumination, the adapter and the electronic flash devices can be conveniently disposed at arbitrary positions. As the adapter, a stand-alone adapter and an adapter built in an electronic flash device are available. As an example of an adapter built in an electronic flash device, Japanese Laid-Open Utility Model Application No. 56-3527 is known.
For the purpose of energy savings of an electronic flash device, some electronic flash devices have a power mode, a so-called standby mode, for turning off the power supply of an electronic flash device after a non-operation state continues for a predetermined period of time.
However, when a slave unit is independent from an electronic flash device, their power supplies must be independently controlled since these power supplies are also independent from each other.
In the above-mentioned prior art, when the slave unit is built in the electronic flash device, and the device has a standby mode function, a problem which is not experienced so far is posed. For example, when the electronic flash device set in a slave mode is set solely, since a non-operation state continues, the power supply of the electronic flash device is automatically turned off, and cannot be synchronized with light emitted by a master flash device in a required photographing operation.
In some underwater electronic flash devices, the number of switches is limited to guarantee a waterproof effect. Therefore, in some devices, the standby mode and the slave function mode may be set by a single member, and hence, these modes cannot be set simultaneously.
Since a normal electronic flash device need not adopt a waterproof mechanism, a slave function setting switch and the like can be disposed at a relatively free position. In conventional devices, a light-receiving portion is normally disposed on a surface in the same direction as a light-emitting portion. When the slave function setting switch is disposed in the vicinity of the light-receiving portion, the meaning of the switch is easy to understand for a user, and an electronic flash device which is easy to use can be provided. In this case, since the power switch is normally disposed on the rear surface of the electronic flash device, a user may not notice that the electronic flash device is set in a standby state, and may complete only the setting operation of the device. Therefore, the above-mentioned problem that the device cannot be synchronized with light emitted by the master flash device in a photographing operation tends to be posed.
On the other hand, as disclosed in Japanese Laid-Open Patent Application No. 55-153927, a delay circuit is arranged between a photosensitive element and a switching element.
In the above-mentioned prior art, when a slave unit is built in an electronic flash device, and a slave circuit with a delay circuit is also proposed, a problem is posed upon switching between a conventional slave mode without any delay time and a slave mode with a delay time like in Japanese Laid-Open Patent Application No. 55-153927 in a single electronic flash device.
For example, a case will be examined below wherein the above-mentioned modes as the slave functions are switched by a normal arrangement, as shown in FIGS. 10 and 11.
Referring to FIG. 10, a slave function setting switch 6 has positions "S" and "D" corresponding to S and D modes (to be described later), and a position "OFF" at which no slave function is selected. In the S mode, slave emission is performed in real time in response to an optical signal; in the D mode, slave emission is performed after an elapse of a given delay time. Since there are three modes including the OFF mode, a microcomputer (to be referred to as a CPU hereinafter) requires 2-bit input ports. A port POUT of the CPU is an output port for outputting a synchronous signal for slave emission to a transistor on the output side.
When a light-receiving circuit SLV.sub.-- CKT supplies an input to an interrupt input terminal INT.sub.-- SLV of the CPU, interrupt processing shown in FIG. 11 is executed to perform slave emission. Note that # in FIG. 11 represents a step.
Referring to FIG. 11, during the interrupt processing starting from #60, since this electronic flash device has a plurality of slave emission modes, the mode must be discriminated in #61. Only when the S mode is selected, an output is generated from the port POUT to realize slave emission in #62. However, due to the presence of #61, the slave emission is delayed by the execution time of this decision step. Since the conventional device has a hardware arrangement, a high-speed response is realized. However, recently, a microcomputer is used too often at the cost of the high-speed response.,
If the high-speed response is disturbed, especially when a small amount of light is to be emitted, only the light emission by the master flash device is performed first, and the degree of contribution of a slave-side electronic flash device is considerably lowered upon automatic light control. As a result, a multiple-flash effect cannot often be obtained.